An emerging body of work focuses on patterns of alcohol consumption during specific events, rather than over a general time period (i.e. past month drinking). Within the event-level literature, 21st birthdays have emerged as the single event that by far conveys the greatest risk for excessive alcohol consumption. While the harms of 21st birthday drinking have been established, few preventive interventions have been tested. Research suggests that personalized normative feedback (PNF) interventions are effective at reducing alcohol use generally, although no stand-alone PNF intervention has been tested for 21st birthday drinking. PNF entails informing a participant where his/her drinking ranks relative to the norm for some population. Typically, students over-estimate the amount of alcohol consumed by others, and correcting this misperception has been shown to reduce drinking. As such, we propose to administer a two-group RCT testing a PNF 21st birthday intervention versus an assessment only control. Given widespread use of mobile phones among college students, the intervention will be delivered via text messaging. Specifically, we will recruit N=28 University of Rhode Island college students turning 21 between summer break of 2016 and winter break of the 2016-2017 school year. Participants randomized to the intervention group will receive two identical PNF text messages sent at 10 A.M. the day before and the day of their 21st birthday celebration, while participants randomized to the control group will not be contacted. The day after their 21st birthday celebration, participants will be emailed a follow-up survey assessing alcohol consumption during their celebration. No other study has examined the feasibility of text messaging as an intervention modality for event level alcohol use; Aim 1 of the current project is to do so. We will also examine whether the intervention is effective at reducing 21st birthday estimated Blood Alcohol Content (Aim 2), and whether the effect is mediated by changes in perceived 21st birthday drinking norms (Aim 3a). Finally, we will examine whether group identity moderates the effect of the putative mediator (moderated-mediation) (Aim 3b). The overarching goal of this study is to test a novel, highly disseminable intervention aimed at reducing extreme levels of alcohol use during a specific event in which excessive drinking often occurs. As such, this research has the potential to reduce serious alcohol-related harms, and can provide a foundation for further 21st birthday preventive interventions in college and non-college populations.